Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0226—Hot rolling
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/005—Ferrite
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips

Definitions

• the present invention relates to a high-strength refractory steel excellent in weldability and gas cutting property and a method for producing the same.
• This fireproof steel is mainly so-called 400MPa class steel or 490MPa class steel, and there are several examples of loose 590MPa class steel with yield strength of 440MPa (45kgf / mm 2 ) or more.
• the Mo content is low.
• the present invention has been made in view of the above circumstances, and is excellent in weldability and gas cutting properties, and has a high yield strength even in an environment exposed to a high temperature such as a fire.
• the purpose of the present invention is to provide a high-strength refractory steel excellent in weldability and gas-cutability and capable of supplying a large amount of high-tensile steel of 440 MPa or more at low cost and a method for producing the same.
• the gist of the present invention is as follows.
• the weld crack susceptibility composition P represented by 0 + 5B is 0.25% or less
• the balance consists of iron and inevitable impurities
• the area fraction of polygonal ferrite or pseudo-polygonal ferrite at the 1/4 thickness position in the thickness direction of the final rolled steel sheet is 10% or less, and is a high-strength refractory steel with excellent weldability and gas cutting properties. .
• a slab or slab having the steel composition according to any one of (1) to (4) is heated to a temperature of 1100 to 1300 ° C, and then a temperature of 800 to 950 ° C After rolling at, the steel is directly quenched at a temperature 150 ° C lower than the temperature at the end of rolling or 750 ° C, whichever is higher, and then Ac (austenite begins to form during heating) (Temperature)
• the weld crack susceptibility composition P represented by Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B is 0.25% or less, and the balance is iron and Inevitable impurities
• the area fraction of polygonal ferrite or pseudopolygonal ferrite at the 1/4 thickness position in the thickness direction of the steel sheet of the final rolling is 10% or less.
• a high-strength refractory steel a high-strength steel with a yield strength of 440 MPa or more that has excellent weldability and gas-cutting properties, and has sufficient high-temperature strength even in environments exposed to high temperatures such as fires. A large amount can be supplied at low cost.
• the high-strength refractory steel of the present invention is not only a building structure, but also a general welded structure steel for civil engineering, offshore structures, ships, various storage tanks, industrial equipment such as thick plate mills, etc. As such, it can be applied to a wide range of uses.
• the high-strength refractory steel of the present invention has sufficient high-temperature strength even in harsh environments such as being exposed to high temperatures such as in a fire, so it has become possible to further improve the safety of welded structures. .
• a steel piece or a slab having the steel composition of the present invention is heated to a temperature of 1100 to 1300 ° C.
• the temperature is 150 ° C lower than the temperature at the end of rolling, the temperature is 750 ° C, the deviation is higher, or the temperature is higher than the temperature. It is directly quenched and tempered at the temperature below Ac in the next stage, so it has excellent weldability and gas cutting performance.
• high-tensile steel with a yield strength of 440 MPa or more which has sufficient high-temperature strength even in environments exposed to high temperatures such as fires, can be produced in large quantities and at low cost.
• a steel slab or slab having the steel composition of the present invention is allowed to cool after hot rolling. Then, it is reheated to a temperature of 900 to 950 ° C. and quenched, and then tempered at a temperature equal to or lower than Ac.
• High tensile strength steel with a yield strength of 440 MPa or more that has excellent weldability and gas cutting properties, and has sufficient high-temperature strength even in environments exposed to high temperatures such as fires.
• the weld crack susceptibility composition P represented by 0 + 5B is 0.25% or less
• the balance consists of iron and inevitable impurities
• the area fraction of polygonal ferrite or pseudo-polygonal ferrite at the 1Z4 thickness position in the thickness direction of the steel sheet of the final rolling is 10% or less.
• the lower limit of 0.04% is the minimum amount for securing the strength and preventing the heat-affected zone such as the weld from softening more than necessary.
• the upper limit of C content is set to 0.14%.
• Si affects the cleanliness, weldability, and weld toughness of steel, it is important to regulate the upper limit. Therefore, the Si content is set to 0.50% or less. Si is also effective in deoxidizing steel. However, since deoxidation of steel is possible even with Ti and A1, it is not always necessary to add Si, especially when weldability and weld toughness are strongly required.
• Mn is an element indispensable for securing strength and toughness, and its lower limit is 0.50%. However, if the Mn content is too high, the hardenability of the steel is increased, which not only deteriorates the weldability and weld heat affected zone toughness, but also promotes the center segregation of the continuous forged slab. %.
• P is an impurity in the steel of the present invention, and if the P content is reduced, grain boundary fracture in the weld heat affected zone is reduced, so the lower the content, the better. Therefore, in order not to deteriorate the low temperature toughness of the base metal and the weld heat affected zone, the upper limit was set to 0.020%.
• S is an impurity in the steel of the present invention, and the lower the content, the better the low temperature toughness of the steel material. Therefore, the upper limit was set to 0.010% in order not to deteriorate the low temperature toughness of the base metal and the weld heat affected zone.
• Nb is an element having an important role in the present invention that suppresses Mo as much as possible.
• Nb increases the recrystallization temperature of austenite and It is an essential element for exerting the effect of controlled rolling. To bring out these effects.
• the steel must contain at least 0.01% Nb.
• Nb contributes to the refinement of heated austenite at the time of reheating prior to rolling, and further has an effect of improving the strength as precipitation hardening, and also contributes to the high temperature strength by the composite additive with Mo.
• the upper limit of the Nb content is set to 0.05% so as not to cause toughness deterioration of the weld.
• Mo is an indispensable element for securing the high temperature strength of steel, and is one of the most important elements in the present invention.
• A1 is a deoxidizing element
• S or Ti is sufficient for deoxidizing steel
• the lower limit is not limited in the steel of the present invention.
• the upper limit is set to 0.060%.
• N is a force contained in steel as an inevitable impurity. It combines with the above Nb to form a carbonitride and enhances the strength of the steel. In addition, when Ti described later is added, TiN is formed to increase the strength of the steel. In order to obtain such an effect, the content of N must be at least 0.001%.
• Ni content is more than half the Cu content
• Cr 0.05-: 1.0%
• V 0.01-0.06%
• B 0.0002-0.0030%
• Ti 0.005-0.025%
• Mg 0 It is preferable to contain one or more selected from 0002 to 0.0050% group strength.
• the main purpose of adding these elements to the above basic composition is as follows. This is to improve properties such as strength and toughness without detracting from the excellent characteristics of steel. Therefore, the amount of added force is limited.
• Ni improves the strength and toughness of the base material without adversely affecting the weldability and weld heat affected zone toughness. In order to exert these effects, it is necessary to contain at least 0.05% or more. On the other hand, excessive addition is not preferable for weldability which only increases the price of steel. Therefore, the upper limit was made 1.0%.
• the Ni content When adding Cu, to prevent Cu-cracking during hot rolling, the Ni content must be within the above range and at least half the Cu content. There is power S.
• Cu exhibits the same action and effect as Ni.
• the upper limit for Cu content is 1.0%.
• the lower limit was set to 0.05%.
• Cr improves both the strength and toughness of the base material.
• the upper limit was made 1.0%.
• the lower limit was set to 0.05%.
• Ni, Cu, and Cr are effective for improving not only the strength and toughness of the base material but also the weather resistance.
• V The effect of V is small compared to the force Nb, which has almost the same action as Nb. V also affects hardenability and contributes to improving high temperature strength.
• B segregates at austenite grain boundaries and suppresses the formation of ferrite, thereby improving the hardenability of the steel and improving the strength. In order to exhibit this effect, it is necessary to contain at least 0.0002%. However, if the content is too large, not only the effect of improving hardenability is saturated, but also B precipitates that are harmful to toughness may be formed. Therefore, the upper limit was made 0.003%.
• stress corrosion cracking is a concern for steel for tanks, etc., it is often important to reduce the hardness of the base metal and weld heat affected zone. For example, hardness of HRC ⁇ 22 (HV ⁇ 248) is essential to prevent sulfide stress corrosion cracking (SSC). In such a case, the additive B for increasing the hardenability is not preferable.
• Ti is preferably added when high toughness is required for the base metal and the weld.
• the reason for this is that when Ti has a low A1 content, for example, when the A1 content is 0.003% or less, it combines with O to form a precipitate mainly composed of Ti 2 O, and an intragranular transformation.
• Ti combines with N to form fine precipitates in the slab as TiN, which is effective in suppressing coarsening of austenite grains during heating and reducing the rolling structure.
• the fine TiN present in the steel sheet refines the weld heat affected zone structure during welding.
• Ti must be at least 0.005%.
• excessive Ti forms TiC and lowers the low temperature toughness and weldability, so the upper limit of Ti content is 0.025%.
• Mg is refined by suppressing the growth of austenite grains in the weld heat affected zone. As a result, the welded portion can be strengthened. In order to exhibit such effects, Mg needs to be 0.0002% or more. On the other hand, when the content is increased, the rate of increase in the effect is smaller than the increase in content, which is not a cost-effective measure. Therefore, the upper limit is set to 0.0050%.
• the high-strength refractory steel of the present invention includes:
• the mass 0/0, Ca:. 0. 0005 ⁇ 0 0040%, REM (Rare Earth Metal):. 0. 0 005 ⁇ 0 preferably contains one or two or any force 0100% of.
• rare earth metals such as Ce, La, and Nd can be used.
• Ca and REM control the morphology of MnS and improve the low-temperature toughness of the base metal. It has the effect of reducing cracking sensitivity. In order to achieve these effects, it is necessary to contain at least 0.0005%.
• the Mo amount is 0.70.
• a yield strength of 440 MPa or more at less than / o and a yield strength at 600 ° C of 2/3 or more of that at room temperature that is, 294 MPa or more, not only the steel components but also the micro It is necessary to limit the organization at the same time.
• the area fraction of polygonal ferrite or pseudo-polygonal ferrite at the 1/4 thickness position in the plate thickness direction of the steel plate of the final rolling is 10% or less.
• the microstructure refers to that at the 1/4 thickness position in the sheet thickness cross-section direction in the final rolling direction of the steel sheet.
• CM weld cracking susceptibility composition P is an indicator of weldability, the lower the better.
• weld cracking susceptibility composition P is 0.25% or less, excellent high temperature strength
• the high-strength refractory steel of the present invention is produced by one of the following first and second production methods.
• a steel piece or a steel piece having the steel composition of the present invention is heated to a temperature of 1100 to: 1300 ° C and then rolled at a temperature of 800 to 950 ° C.
• This is a method in which direct quenching is performed at a temperature 150 ° C lower than the temperature at the end of rolling or 750 ° C, which is higher, and then tempering is performed at a temperature equal to or lower than Ac.
• a slab or slab having the steel composition of the present invention is hot-rolled, allowed to cool, then re-heated to a temperature of 900 to 950 ° C., and then quenched. Below temperature
• a slab or slab having the steel composition of the present invention is heated to a temperature of 1100 to: 1300 ° C.
• the reason why the heating temperature prior to rolling is limited to 1100 to 1300 ° C. is that the austenite grains during heating are not made larger than necessary, and the rolling force is also refined.
• 1300 ° C is the upper limit temperature at which the austenite during heating does not become extremely coarse. If the heating temperature exceeds this upper limit temperature, the austenite grains become coarsely mixed and the rolled austenite grains become relatively coarse. As a result, the phase transformation from coarse-grained austenite that not only makes the metal structure after phase transformation relatively coarse, but also the microstructure becomes fragile and the toughness of steel easily deteriorates.
• the lower limit of the heating temperature was set to 1100 ° C in consideration of the effect of controlled rolling during hot rolling and the solutionization of Nb to develop precipitation hardening.
• the steel piece or the slab piece heated in this way is rolled at a temperature of 800 to 950 ° C.
• the reason for limiting the rolling temperature to 800 to 950 ° C is that when rolling is performed at a temperature exceeding 950 ° C, the refinement of rolled austenite is reduced despite the combined addition of Mo and Nb. This is because even if direct quenching and tempering are performed afterwards, it is difficult to ensure low temperature toughness stability.On the other hand, if the temperature is below 800 ° C, the ferrite will be directly quenched even though it depends on the plate thickness. This is because it becomes difficult to secure a microstructure, and Nb precipitates during rolling and does not contribute to high temperature strength.
• quenching is performed directly at a temperature 150 ° C lower than the temperature at the end of rolling (rolling end temperature is 150 ° C) or higher than 750 ° C, which is higher.
• the reason for limiting the direct quenching temperature as described above is to secure the microstructure first. This is because the microstructure is controlled for the purpose. To that end, it must be at least 750 ° C. However, even if the temperature is higher than 750 ° C, if there is a temperature drop exceeding 150 ° C from the rolling end temperature, the possibility of recovery after rolling 'recrystallization' or precipitation of Nb increases. May cause a decrease in strength.
• the direct quenching start temperature was limited to the rolling end temperature—150 ° C or 750 ° C, whichever is higher.
• tempering is performed at a temperature of Ac or lower.
• the steel slab or slab having the steel composition of the present invention if it is generally 700 ° C or less, it is Ac or less, and the actual processing temperature is set according to the purpose such as strength.
• the temperature of tempering is about 450 to 650 ° C.
• These rolling temperatures and the like are steel plate surface temperatures that can be monitored.
• the high-strength refractory steel of the present invention can be manufactured.
• the steel piece or slab having the steel composition of the present invention is allowed to cool after hot rolling.
• each condition of hot rolling and cooling is not particularly limited.
• the reason is that the metal structure and material strength of the steel slab or slab are determined by the subsequent reheating quenching and tempering process.
• This reheating 'quenching temperature is defined by the metallurgical definition of Ac
• the temperature above Ac is 900 ° C.
• the maximum temperature for reheating and quenching was set to 950 ° C.
• tempering is performed on the reheated / quenched steel pieces or steel pieces at a temperature equal to or lower than Ac.
• the conditions for this tempering process are exactly the same as in the first manufacturing method described above.
• the high-strength refractory steel of the present invention can be manufactured.
• the high-strength refractory steel of the present invention can be applied to a wide range of uses as a general welded structural steel, such as civil engineering, offshore structures, ships, various storage tanks, as well as building structures.
• yield strength As mechanical properties, yield strength, tensile strength, and yield strength at 600 ° C were measured, and the yield ratio (yield strength / tensile strength (%) was calculated from the yield strength and tensile strength. )) was obtained and evaluated.
• a 2 mm V notch impact test specimen specified in the Japanese Industrial Standard JI S Z2202 “Metallic material impact test specimen” was taken from the center of the thickness in the direction perpendicular to the rolling direction.
• the fracture surface transition temperature (vTrs (° C)) of the impact test piece was measured and evaluated based on the industrial standard JISZ 2242 “Metallic material impact test method”.
• the gas cut surface roughness is specified in Japanese Industrial Standard JIS B 0601 “Product Geometric Characteristics (GPS) —Surface Properties: Contour Curve Method—Terminology, Definitions and Surface Properties Parameters” for the surface of the steel sheet.
• GPS Product Geometric Characteristics
• the maximum height (Ry) of the measured surface roughness was measured, and when this maximum height (Ry) was 50 ⁇ m or less, it was evaluated as “ ⁇ ”, and when it exceeded 50 ⁇ m, it was evaluated as “X”.
• the target values for each characteristic are: yield strength is 440 MPa or more, fracture surface transition temperature (vTrs) is _40 ° C or less, yield strength force at 600 ° C is 3 ⁇ 494 MPa or more, and absorbed energy (vE) at 0 ° C is
• Table 1 shows the steel composition
• Table 2 shows the steel plate manufacturing process and characteristics.
• the present invention by adding Nb while suppressing the Mo content, it is possible to stably secure high-temperature strength in a high-strength steel having a yield strength of 440 MPa or more, and by suppressing the Mo content, Degradation of gas cutting ability is minimized, and at the same time, the amount of individual alloying elements and P including C, Si and Mn are limited.

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• 2005
  • 2005-03-04 JP JP2005060601A patent/JP4718866B2/ja active Active
• 2006
  • 2006-03-03 WO PCT/JP2006/304127 patent/WO2006093282A1/ja active Application Filing
  • 2006-03-03 KR KR1020077017575A patent/KR100920536B1/ko active IP Right Grant
  • 2006-03-03 US US11/816,015 patent/US20090025839A1/en not_active Abandoned
  • 2006-03-03 TW TW095107217A patent/TWI322830B/zh not_active IP Right Cessation
  • 2006-03-03 CN CNB2006800036308A patent/CN100529139C/zh not_active Expired - Fee Related

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